This application is a reissue patent application of U.S. patent application Ser. No. 09/156,171 filed Sep. 17, 1998, now U.S. Pat. No. 6,033,564; which is a continuation-in-part application of U.S. patent application Ser. No. 09/115,527 filed Jul. 13, 1998, now U.S. Pat. No. 6,312,610. 
The pertinent field of the invention is the xe2x80x9cimperforate bowl,xe2x80x9d related to prior art under xe2x80x9cfluid separation,xe2x80x9d especially xe2x80x9cDisk Centrifuges,xe2x80x9d xe2x80x9cNozzle Centrifuges,xe2x80x9d and xe2x80x9cSplit Bowl Centrifugesxe2x80x9d
Within the scope of this application, prior art is taken to mean conventional methods of construction for the outer walls of centrifuges. One such method for such design, fabrication and assembly predominates for all major types or classes of imperforate bowl centrifugal devices, including notably: (1) those used to separate small volumes of materials, such as Test Tube, Tubal, Preparatory and Zonal Centrifuges; and (2) those used to process industrial volumes of materials, including Decanting Centrifuges, and Disc Centrifuges. Disk type imperforate bowl devices further break down into Manual Discharge, Intermittent Discharge (Split Bowl and Valve Nozzle), and Continuous Discharge (Open Nozzle) models.
To put the conventional methods of centrifuge outer wall construction into perspective, this application refers to one particular reference work regarding methods of manufacture, which is: Fundamental Principles of Manufacturing Processes, by Robert H. Todd, Dell K. Allen and Leo Alting, Industrial Process, Inc., New York, N.Y., 1994.
For nearly 100 years, the one highly predominant method of centrifuge fabrication for all three types of imperforate bowl devices has been their fabrication in steel, stainless steel, and various other steel alloys. Such metal construction requires fabrication methods including xe2x80x9cshapingxe2x80x9d via xe2x80x9cmass-reducingxe2x80x9d, primarily through xe2x80x9cmechanical reducing,xe2x80x9d techniques such as turning, carving, lathing, milling and drilling. (See FIGS. 3 and 4, which are reproductions of page 8 and 9 of the referenced work).
This often-cited reference work places each means of construction, as of 1994, into a hierarchical taxonomy of manufacturing methods. In its introduction to this taxonomy, the authors state:
The Manufacturing Processes Taxonomy, based on the process classification method initially developed at Brigham Young University and later adapted by members of the Manufacturing Consortium, provides a precise roadmap of some 300 processes used for modifying geometry or properties of engineering materials. It has been said that students can learn twice as much in half the time when the material to be studied has been classified and the critical attributes have been clearly identified. In this text we attempt to do both. Processes used for modifying workpiece geometry [italics from the authors] are called xe2x80x9cshaping processes.xe2x80x9d Processes used for modifying properties [italics from the authors] are called xe2x80x9cnonshapingxe2x80x9d processes. (Page 6).
Thus, the objective of this book is to assist industrial designers by informing them of all possible construction avenues, and of the tradeoffs inherent in each type of material and method of construction, so as to pro-actively achieve maximum appropriateness and cost-effectiveness in their finished goods. Or, as stated in Chapter 1.
In manufacturing, the actual materials and equipment used are costly, but these costs are substantially determined by those responsible for product design before manufacturing even begins. By virtue of decisions made early in the production process, designers determine up to 70 percent of manufacturing costs.xe2x80x9d (Page 1).
Not surprisingly, many long-established industrial goods still being produced today were originally designed using the material choices and manufacturing methods developed during the industrial revolution. This is true in general of products fashioned in metal, and specifically of imperforate bowl centrifuge.
Because of the century-long tradition of building centrifuges in metal, one can accurately describe the metal manufacturing techniques used by imperforate bowl device builders as the xe2x80x9ctried and truexe2x80x9d fabricating methods for this industry.
As interesting xe2x80x9ctried and truexe2x80x9d phenomenon occurs in manufacturing. If, at any given point in time, you only have certain ways to build something, then the things you can build in those ways are what get built. Then, because of the things you have gotten used to building, you cease looking for different ways to build, because you already have a successful product, done xe2x80x9cthe way you already do it.xe2x80x9d This phenomenon goes to the heart of the patent issue of non-obviousness. If the many advantages of other-than-metal construction were obvious to experts in the field of imperforate bowl centrifuges, such constructions would be patented, commercially available, and, in view of their claimed cost and performance superiority, even prevalent in the field. By contrast, what we see instead in the field of the industrial-volume imperforate bowl is steel and alloy centrifuges.
The inventors do not claim that conventional centrifuge construction via conventional metal-crafting has no place in many traditional products. But it is clear that a wealth of superior new material and fabrication methods for the highly stressed outer walls of centrifuges has become available, particularly since the 1970""s, and that this wealth to date has been all but ignored by centrifuge makers, particularly by manufacturers building industrial-volume devices. Such manufacturers are busy building existing steel and alloy walled devices, xe2x80x9cthe way they are used to building them.xe2x80x9d They do not appear to be exploring radical new hybrid or composite construction methods for their imperforate bowl products.
These realizations led to a key design decision on the part of the inventors of the Density Screening outer wall transport system pending U.S. patent application Ser. No. 09/115,527. This decision was to explore the possible benefits to be obtained from a complete rethinking of the materials and methods of construction for the outer, collecting walls of centrifuges, from the point of view of works such as Fundamental Principles of Manufacturing Processes.
This decision posed the initial manufacturing philosophy question: xe2x80x9cIf you were inventing centrifuge afresh, today, and you had the entire breadth of old and new manufacturing processes at your disposal, what materials and what manufacturing methods would you select?xe2x80x9d Again, this is not a question the traditional device builders appear to have asked. When the benefits of such a rethinking become apparent, it is clear that the traditional metal fabrication mindset of centrifuge builders has prevented them from seeing the obvious: that selected new materials offer extraordinary new benefits and advantages, including both greatly increased strength and far lower cost.
As research and design work continued, several related secondary questions emerged. These were: (1) Is it possible to conceptually filet a centrifuge outer wall into different layers, and then define the unique physical functions and properties ideal to achieve in early layer? (2) Would it then be desirable and practical to employ radically different materials and manufacturing methods for each such individual filet or layer of a centrifuge outer wall, so that each such member provided the ideal mix of physical characteristics and cost performance for that layer? And, (3) Might it then also occur that all of said ideally fabricated individual layers, when combined together, yield an overall design strategy far superior, both in physical characteristics and cost performance, to traditional design and construction methods, for centrifuge outer collecting walls?
The rich, multiple answers to the first question led the inventors to discard conventional manufacturing wisdom and techniques for the product in question. The answer to the secondary questions also turned out to be resounding xe2x80x9cyes""s,xe2x80x9d which answers then led to the hybrid fusion of variably-fabricated outer wall elements, each constructed using a different technology, which is the method of construction claimed in this application. This design fusion also characterizes and made possible the Density Screening outer transport wall geometry method claimed pending U.S. patent application Ser. No. 09/115,527.
In a nutshell, the inventors first realized that, if all required physical and structural requirements for centrifuge outer walls could be achieved by building centrifuges of a combination of (1) castings made of relatively inexpensive aluminum or ceramic, (2) chemically hardened wear surfaces, (3) plastics and (4) high-tensile strength reinforcing fibers, the resulting devices should be far less expensive than traditional art built of high-strength steels or alloys.
As the hybrid or sandwich construction method developed, the inventors further realized that these methods enable the design and construction of centrifuge outer wall geometries that are either not possible, or prohibitively expensive to do in conventional metal. The first utility patent filed covered these new, material-facilitated geometries, while this application claims the composite means of construction which makes those geometric possible.
Review of Three Classes of Centrifuge, All Constructed In Cast and Carved Metals
Tubal centrifuges are usually small-scale, laboratory devices constructed of a cylindrical metal outer wall enclosing the fluid work area, which in turn surrounds a conventionally constructed metal solid core. Some tubal centrifuges add vertical metal vanes, radiating from the solid core to the interior of the outer wall cutting through the fluid work area to vertical fluid separation zones; such centrifuges are thus called zonal centrifuges.
Decanting centrifuges are high volume workhorses for applications such as wastewater treatment and oil platform fluid recycling. These are long and narrow devices, in either vertical or horizontal configuration, and are also built of metals using traditional casting, milling and carving methods. The transport solution in Decanting Centrifuges is a tight-fitting helical screw fitted against the inside of the outer wall, which scrapes out heavy materials being thrown and held against that outer wall by centrifugal force. Among the numerous examples of decanting centrifuge prior art, including decades of improvement patents for various forms of multi-speed transmissions, wear-surface improvements and the like, are: U.S. Pat. Nos. 3,937,317, 3,960,318, 3,967,778, 3,977,515, 4,070,290, 4,251,023, 4,298,162, 4,379,976, 4,381,849, 4,504,262, 4,519,496,4,581,896, 4,978,331, 5,197,939, 5,374,234, 5,380,434, 5,397,471 and 5,429,581. The foregoing is a representative, but by no means exhaustive, list of such prior work.
Disk Centrifuges. This third class of centrifuges approaches high volume in continuous operation in a more design-elegant way, through the use of the pure geometry in the form of the heavy material receiving shapes in the device""s outer walls. These devices, all within the family of Disk Centrifuges are variously called Continuous Discharge Nozzle, Nozzle-Valve, and Split Cone centrifuges, depending on the details of their heavy particle collection and ejection approaches. From within the large field of prior art for these centrifugal devices, notable are patents U.S. Pat. Nos. 4,005,817, 4,015,773, 4,067,494, 4,103,822, 4,311,270, 4,343,431, 4,375,870, 4,505,697, 4,629,564, 4,743,709, 4,698,053, 4,701,158, 4,710,159, 4,721,505, 4,719,759, 4,759,744, 4,813,923, 4,820,256, 4,840,612, 4,861,329, 5,045,049, 5,052,996, 5,202,024, and 5,362,292. Again, the preceding list is not intended to be exhaustive, but rather illustrative of the disk centrifuge approach and some of the many attempts by numerous inventors and manufacturers to improve it over the years. All the Disk type centrifuges also employ conventionally cast, carved, polished and turned meal outer walls, which walls are generally fashioned as a pair of upper and lower bell-shaped shells which flare out at their beltline connecting point.
Two Primary Centrifuge Outer Wall Material Considerations
(1) Abrasion-Resistance (Hardness)
The two primary qualities addressed in conventional, metal-constructed centrifuge outer walls are wear-resistance, and bursting or hoop strength. To put these two qualities in proper perspective, it is helpful to first review the operating environment and physical requirements for centrifuge outer walls.
First, regarding wear surfaces, centrifuge interiors in general and particularly the interior surface of the outer wall of a centrifuge, are an extremely punishing and hostile environment for any chosen construction materials. The outer wall of any centrifuge is constantly bombarded by abrasive, heavy materials, made many times heavier and more abrasive than they would be at rest by the action of centrifugal force. The effect is similar to that of continuous heavy sandblasting. Thus the first criterion for outer walls in centrifuges is that they be made as abrasion resistant and hard as possible.
Various steel alloys, and sometimes titanium, used in tubal, decanting and disk centrifuges, supply sufficient hardness to permit the ongoing sale and use of large numbers of practical, commercial machines. However, newer technologies exist which would permit the construction of interior wall surfaces having many times the hardness or abrasion-resistance of the hardest metals.
(2) Burst or Hoop Strength
Bursting or hoop strength is, as the name implies, the ability of a vessel to maintain its structural integrity despite internal pressures or centrifugal forces acting upon that vessel.
The outermost diametric zones of centrifuges receive the highest gravitational forces within any given device. (The further out from the axis of rotation you are, the higher are the centrifugal forces.) This phenomenon is a function of the basic physics of centrifugal force; one of many sources which document this fact is the Laboratory Monograph, xe2x80x9cUltra-Centrifugation,xe2x80x9d by J. S. McCall and B. J. Potter, as illustrated in FIG. 5 (text annotation in FIG. 5 is a direct quote of the illustration legend in this reference work).
Thus, centrifuge outer walls fabricated of conventionally fabricated steels, titaniums and various metal alloys not only must have sufficient bursting or hoop strength to hold together as their own weight is increased many hundreds or thousands of times by centrifugal force, but also must exhibit strength beyond this, to contain the heavy materials being thrown against them from the centrifuge core. These materials also weigh hundreds or thousands of times their at-rest weight.
The outer wall of centrifuges must therefore resist and contain cumulatively the amplified weight of the wall itself plus the thrown weight of the heaviest materials being processed. As is the case with hardness and abrasion-resistance, all three types of commercial centrifuges have successfully employed metal materials and fabrication technologies in support of outer walls of sufficient strength to work within existing device paradigms. Review of both prior art patents and available product literature for all types of centrifuges reflects the decades of engineering experience in the form of a mature traditional wisdom regarding the maximum diameters for metal centrifuges. These diameters are a function of the maximum rotational speed to be employed in a given unit.
To reiterate, the broader the diameter of a centrifuge, the more gravitational or bursting force is placed on those components of that centrifuge which are furthest out from the axis of spin, which components are always the outer wall. The diameter limits of metal centrifuge bursting strength, regardless of how the material is fabricated and finished, appears to be in the area of 36 to 48 inches for relatively low-gravity devices (producing up to 2,500 to 3,000 gravities), down to much smaller devices, such as five to 10xe2x80x3 in diameter, for devices operating in the ultracentrifuge range (tens of thousands of gravities or higher).
To put this yet another way, a centrifuge outer wall of a given outer diameter (xe2x80x9cxxe2x80x9d inches) operating at its maximum burst strength RPM""s will likely experience structural failure if that centrifuge""s rotational speed is further increased. And, conversely, a given centrifuge operating at its maximum outer wall burst strength at a fixed RPM will also likely fail at that RPM if its design diameter is further increased.
The well-documented strength ceilings for steel, titanium and alloy metal used in centrifuge outer walls, and the well-known ratios of rotational speed/centrifugal force times diameter which are governed by those limitations, have created widely accepted limitations for the use of centrifuges. On one hand, it is clearly possible with existing materials and (metal) fabrication methods to build devices which process very small quantities of fluid (pints or quarts) at comparatively high gravities (in small diameter devices such as tubal or zonal centrifuges). And, on the other hand, it is also possible build devices, such as industrial disk or decanter centrifuges, which process much larger quantities of fluid (hundreds of gallons), but only at much, much lower gravities.
What appears not to be possible using the decades-old metal based methods of construction and assumptions inherent to all conventional centrifuges is the processing of comparatively large volumes of fluid at centrifugal forces well above approximately 2,500 to 3,000 gravities. This cannot presently be done because metals cannot provide sufficient hoop or bursting strength to contain the heavier, high volumes, in large diameters, at higher gravities.
Societal Ramifications of the Limitations of Prior Art Outer Wall Fabrication Methods
Many of today""s most pressing environmental problems present very high processing volumes combined with extremely fine, light (and often very dangerous, i.e., cryptosporidium cysts in water supply) particles requiring separation. This is exactly the combination which conventional, metal-fabricated centrifuges cannot economically supply, namely, high-volume processing at high enough centrifugal forces (estimated at 8,000 gravities) to remove xe2x80x9cparticlesxe2x80x9d down to the one-half micron range. The current (summer 1998) shutdown of the municipal water system in Sydney, Australia, due to the takeover of that supply by mutated, chlorine-resistant, very small bacteria is but the latest example of such growing environmental problems.
The one exception to the blanket statement that industrial-volume centrifuges cannot remove ultra-small particles is the expensive, mechanically elaborate disk centrifuge, which uses the amplifying effect of stacked disks to produce fine particle separation using lower centrifugal forces, in the realm of 2,500 to 3,000 gravities, some models of which can remove particles in the sub-micron range. However the very high initial cost of and extensive ongoing maintenance required by each of these centrifuges has so far inhibited their use in large arrays of many of such devices, as would be required, for example, to continuously treat all the drinking water for a large metropolitan area.
In the absence of affordable, large-volume, very high speed, ultra-small particle removing centrifuge, chemical additives plus filtration has become the hybrid treatment of choice for large-volume water supply treatment, even though the problems of membrane clogging, filter cleaning, replacement cost and the landfill storage of used filters keep chemistry plus filtration from appearing to be the ideal or elegant long-term solution for water treatment. In addition, more and more long-term health disadvantages of the use of chemicals in water, both individually and from the side-effects of their combinations, are coming to light. These widespread and intractable disadvantages further underscore the desirability of cost, strength, volume and operating breakthroughs in centrifuge design generally, as dictated by centrifuge outer wall design specifically.
To summarize, laboratory tubal centrifuges can gravitationally separate out the kinds of ultra-small, ultra-light particles which plague the nation""s water supply, but only in test-quantity sizes. Those disk centrifuges which use stacked disk cores to amplify gravitational separation can separate quite small particles from fluids, in industrial size quantities, due to that amplification technique allowing the use of rotational forces below 3,000 gravities; however, such extremely complex, and maintenance-intensive devices cost many hundreds of thousands of dollars each. Again, they have not been adopted for large scale fluid separation such as water treatment, most likely because they are not cost-effective for such mass use. Finally, commercial decanting centrifuges"" upper centrifugal limits in the 2,500 gravity range, lacking the amplifier effect of stacked disks, cannot remove particles below approximately 3 to 5 microns. And, large volume Decanters are also extremely expensive, approaching one million dollars apiece.
All of the foregoing is to illustrate that the outer wall material chosen for traditional centrifuges has had an enormous impact on these devices"" limitations of use. The inventors of the Density Screening outer wall transport method not only rejected the traditional wisdom of metal outer wall construction, but in so doing, have also rejected the traditionally accepted end-application and cost limitations placed on various types of available centrifugal devices.
Objects and Advantages
When the inventors committed their researches to the re-thinking of the basic material, or materials, used to fabricate centrifuge outer walls, they also became freed up to consider using multiple materials, in a hybrid sandwich, with each layer of material being chosen to do a specific indicated job in the strongest, least expensive way possible.
The researchers chose to emulate or model the sequential trajectory of heavy particles being thrown from the core of a rotating centrifuge, out to and as it developed, through the outer wall of a centrifuge. This intellectual process of following a hypothetical thrown particle, along its journey from the inside of the outer wall to the outside, and assessing the materiel requirements of an ideal centrifuge outer wall at each point of this trajectory, led to the following sequential or layered analysis of the ideal characteristics for each point or layer of this journey.
Water Surface Technology
The primary, explicit job of a centrifuge is to throw heavies outward, thus sorting them away from the lighter fluid flow of the device""s center core. The ejecting heavies, the densest and often most abrasive materials in a given fluid flow, thus constantly bombard the innermost or facing surface of the outer wall of a centrifuge. The inventors"" review of old and new manufacturing materials and of their related fabricated processes, as available in the late 1990""s, led through the manufacturing taxonomy to xe2x80x9cnon-shapingxe2x80x9d, and then to xe2x80x9csurface finishingxe2x80x9d and then to xe2x80x9csurface-coatingxe2x80x9d (see FIG. 3, a reproduction of page 8, Dodd, Allen and Alting, op.cit.).
In-depth review of many different types of xe2x80x9chigh-techxe2x80x9d surface coatings revealed how, among many late 20th century hardening methods, the outer surface of an inexpensive and thin, cast or stamped aluminum part can be transformed, through processes such as xe2x80x9cPhysical Vapor Depositionxe2x80x9d (PVD), into ultra-hard sapphire, or by xe2x80x9cChemical Vapor Depositionxe2x80x9d (CVD) into other extremely hard surfaces. These are but two of several surface coating technologies which can turn a very inexpensive piece of metal or ceramic into a part having many times the abrasion resistance and life expectancy of any comparable metal.
Once the inventors elected to slice the outer centrifuge wall into multiple, thin hybrid sections, the use of technologies such as PVD or CVD for the innermost wear surface, becomes both practical and inexpensive. See FIGS. 1 and 2, Parts 2, for illustration of two iterations of such an innermost wear-surface slice, tile or integral deposited surface, as shown in these illustrations of a single outer wall void segment of a Density Screening outer wall sandwich.
Compression Load Transfer and Support for the Wear Surfaces
Once the strategy of using an inexpensive, thin and hardness-treated wear surface layer was understood, it quickly became clear that the next outermost layer of the evolving centrifuge wall would have to satisfy two physical requirements. First, the thin wear layer would need incompressible physical support by means of the layer immediately outside or behind it. This is the case because the wear layer is not only being bombarded with many extremely heavy, abrasive individual particles being thrown from the centrifuge, but also because it is being subjected to immense, deforming, centrifugal force. This gravitational force being applied to the thin wear surface layer thus dictates the need for a backing layer behind the wear surface, to absorb and transfer the compression load of centrifugal stress.
The second requirement for the middle layer is one of dynamic balance. As stated previously in this application, centrifuges spinning at high speed have extremely low tolerance for weight or density imbalances across the axis of spin. This is the reason that steel and other metal centrifuges are laboriously lathed, turned and otherwise brought into dynamic balance after casting. In the newly developed method of construction for the Density Screening outer transport wall, the second or compression-load transfer layer needs to be designed and manufactured in such a way as to achieve dynamic balance. If such balance can be attained without expensive post-casting machine finishing, so much the better.
Fortunately the age-old manufacturing method of casting, as extensively revised during the late 20th century, has evolved into a technology known as xe2x80x9cinvestment casting.xe2x80x9d This method can mass-produce parts made of aluminum, ceramic and many other materials, notable for both the intricacy of finish it can produce with little or no post-machining, and also for its ability to produce extremely uniform weight and density characteristics in mass-produced parts.
The uniform size and density intrinsic to such parts lends itself exceptionally well to their use as the middle, compression-load-transferring layer of a centrifuge outer wall. This middle layer also comprises the greatest percentage of the mass of the hybrid outer wall assembly. If the casting or castings which comprise this layer are dynamically weight-balanced via precision casting, the cost of producing a balanced assembly is far less than the extensive finishing and balancing methods required for metal centrifuges.
In addition, for some applications, such middle-layer members can be made of extremely incompressible but comparatively lightweight materials such as cast ceramic. If this, the compression-load transfer, layer, of a given Density Screening outer transport wall is exceptionally light, or low in mass, then the total energy required to spin the entire centrifuge is reduced. See FIGS. 1 and 2, Parts 4, for a single outer wall void segment illustration of the compression-load, wear-surface backing layer, in the Density Screening outer wall sandwich.
The Key to Centrifuge Limitation: Bursting Strength
Before describing the outermost layer of the Density Screening outer transport wall, it will be helpful to review the final, most needed material characteristic for centrifuge outer walls. Until now, the limitations of metal-fabricated wall strength available in commercial centrifuges has drawn a line in the sand regarding how large they can be, and how fast they can spin.
As stated previously, metal casting and carving fabrication techniques, as applied to centrifuge design and construction, represent a thoroughly mature technology. Their size and speed limitations as applied to centrifuges are well known. And, as stated above, until now their limitations have governed centrifuge development.
In those parts of such devices having high-strength requirements, such as all parts to be high-speed rotated out away from the axis of spin where centrifugal force is the highest, metal parts is the final assembly of conventional centrifuge walls are often laboriously x-rayed to uncover metal crystal and/or welding flaws which would compromise bursting strength and lead to catastrophic failure at speed.
The extremely high cost of steel and alloyed raw materials certified to have predictable, uniform crystal structure, strength and other qualities, and the equally high cost of casting, turning, finishing, testing and documenting such parts, is well known in the metal trades. In large part because of the costs of raw materials and fabricating, a single large decanting centrifuge can cost a million dollars or more. A single conventional disk centrifuge, also metal fabricated, can cost a quarter million dollars or more.
Smaller tubal centrifuges, again made of cast and carved metals, but of lesser cost because of their smaller sizes, can spin much faster and produce much higher gravities than the other devices, but only because of their deliberately small diameters, which keep the centrifugal forces produced within the available strength of the metals used, but also limit their use to fluids in test or extremely small production quantities.
In centrifugal devices designed to attain comparatively higher rotational speeds, another problem must be addressed, which is harmonics. In a centrifugal device, spinning so as to produce 2,000 or 3,000 multiples of gravity, and filled with extremely heavy fluid whose heavier components are being thrown outwards at greatly increased weights due to gravitational force, harmonics or out-of-phase vibrational forces can quickly cause structural failures. Rotational speeds significantly higher than 3,000 gravities further amplify the need to control harmonics.
Centrifuge device assemblies for high-speed operation must therefore achieve precise dynamic balance, and they must also be torsionally rigid, since twisting forces in a device, particularly during acceleration, can also induce destructive harmonics.
Filament Winding for Unprecedented Bursting Strength and Torsional Rigidity
In the 1960""s, a critical technical review of the state of the art of high-speed, Zonal Centrifuges (xe2x80x9cThe Development of Zonal Centrifuges . . . xe2x80x9d, National Cancer Institute Monographs, Norman G. Anderson, et al., editors, 1966) stated, in part that xe2x80x9cfilament winding,xe2x80x9d then a new technology, could be very profitably applied to the fabrication of stronger, laboratory-size zonal centrifuge rotors. This review stated:
xe2x80x9c . . . it is evident that higher speeds and resulting higher g fields can be produced by using circumferential wraps of fiberglass or steel wire over a liner. This technique has been used by aerospace firms for rocket motor cases and represents the simplest fabrication method. Two slightly different methods have been used to form rocket motor cases. These are (1) the balanced method, which uses sets of longitudinal and circumferential wraps such as those on the Polaris Missile case, and (2) the method of winding the cases on a helix angle where the path of the glass or wire filament is that of a geodesic. Techniques for winding vessels with openings on either end of the cylinder, such as would be required for centrifuges have also been developed for aerospace applications.xe2x80x9d
Interestingly, the present inventors"" extensive review both of patents (1976 to 1998) and of product literature from all major centrifuge makers, reveals no evidence of the implementation of filament-winding technology in centrifuges, except in a very few, small laboratory size rotors, as had recommended in the reference NCI Monograph back in the 1960""s. And more interestingly, no references have be found to using filament-winding, including the use of the radical new, high-strength plastic fibers, to strengthen the outer cases of large industrial centrifuges.
By the late 1990""s filament winding technology has moved beyond the use of high-stress parts by the aerospace industry. Besides being used for rocket motor cases and jet turbine helicopter rotor transmission shafts, filaments winding is now being widely applied to sports equipment (canoe paddles, golf club shafts, bicycle frames) and is being actively explored for other types of manufacture as well.
To achieve unprecedented burst strength and torsional rigidity for the proposed new method for constructing centrifuge outer walls, this application therefore completes the multi-layer hybrid or sandwich construction for Density Screening type centrifuge outer walls, by laying up the outermost layer with filament-winding technology, again, not in evident use in present-day centrifuge fabrication, except for small lab rotors.
Therefore, the outermost member of this hybrid or sandwich method for constructing centrifuge outer walls is a filament-wound, bursting-strength reinforcement layer. See FIGS. 1 and 2, Parts 5, for a depiction of this final, bursting-strength component of the claimed outer wall construction method. FIGS. 1 and 2 also show all four of the layers in sequence, in a cut-away illustration of a single Density Screening outer transport wall collecting void. See also FIG. 6, for a perspective, cut-away half section view, showing these layers as built up with multiple outer wall collecting voids in a typical configuration, and FIGS. 13, 14, 19 and 20 for top views of various centrifugations of the entire hybrid/layered outer wall method.
In addition to the fiber materials cited by Anderson et al. in the late 1960""s, today, for high-strength uses, filament winding has progressed far beyond the use of steel wire or fiberglass. Widespread use is now being made of fibers such as the enhanced nylon used in bullet-proof vests (Kevlar(trademark) [trade name for aramid]), and molecular-chemical fiber products such as graphite and carbon fiber. Kevlar has a documented tensile strength up to five times that of the strongest steel alloy. Commercial carbon fibers (such as those sold by Amoco) can provide tensile strengths up to ten times that of titanium. Carbon fibers, although strongest, are also brittle; Kevlar fibers, less strong, are far more flexible. The uses of mixes of fibers to obtain ideal strength/flexibility characteristics is a maturing and commercially documented material science (See FIG. 27 for a reprint of one several American commercial vendor""s fiber strengths comparison chart, against steel and titanium).
Filament winding converts the extraordinarily high tensile strength of the fibers used into hoop or bursting strength, for whatever vessel is surrounded and thereby reinforced by the fiber, usually affixed in an adhesive resin mixture. The wide range of specialty resins, combined with the available broad range of fibers and fiber mixes, is well known and available from many manufacturers. As a technology, filament winding is rapidly maturing. However, the use of filament winding to dramatically strengthen centrifuge outer collecting walls is herein claimed as both novel and non-obvious to experts in the imperforate bowl field.
Thus it became clear to the inventors that another extraordinary advantage of the hybrid technology, i.e., the multi-layered construction of centrifuge outer walls, obtained from the outermost use of filament winding, is an up to ten-fold increase in available bursting strength, without any use of metals whatsoever for strength.
Filament winding is also the technology of choice in applications where maximum resistance to twisting, or torsional resistance, is desirable. Destructive vibrations or harmonics at high rotating speed can come from many causes, and all will have to be addressed in the design and construction of individual Density Screening wall-surrounded centrifuges.
However, one source of harmonics which the outer, filament-wound layer addresses at the outset, is the torsional twisting of the centrifuge outer wall, particularly during acceleration. Jet helicopter transmission shafts, which must be ultra-stiff to transmit extremely high-torque and high-speed rotational energy to the blades, have been manufactured for many years using filament winding. The torsional rigidity imparted to Density Screening outer walls is therefore a proven added benefit, in addition to the bursting strength multiplying effect already described.
Summary of Objects and Advantages
A centrifuge whose outer wall is a sandwich of several hybrid layers, using the Density Screening outer wall method of construction, will be designed for routine operation at 5,000 to 8,000 gravities. These much higher rotational speeds are obtainable because of the synergistic sum of the various properties of the layers combined: ultra-hardness in the wear surface layer to withstand much higher gravity particle bombardment and abrasion; even weight distribution of lightweight but totally non-compressible castings in the load-transfer layer to manage balance and harmonics engineering problems; and, use of filament-winding as the outermost layer of the hybrid shell wall, to increase bursting strength for the entire assembly five to ten times beyond that of metal-walled centrifuges, while adding unprecedented torsional rigidity.
The hybrid method of construction detailed in the preceding section of this application has yielded an outer wall technology, the Density Screening method of construction, which not only benefits from all of the geometry improvements noted in pending U.S. patent application Ser. No. 09/115,527, but which can also, device by device, deliver as much as ten times more bursting strength that can a steel walled counterpart, while additionally offering the dynamic balancing, stiffness and torsional rigidity qualities required for such extremely high RPM operation. These combinations of strengths will also be achievable at far lower design and construction costs than can be attained via the metallurigical craft construction methods used in prior art.
The combined or synergistic strength features of the method of construction presented, translates to devices using the Density Screening outer wall transport method, and surrounding tubal, decanting or stack-cone cores, buildable to any practical length (for long residence time), and constructable either in larger diameters than is presently practical (thus accommodating larger volumes of fluid processing per device), or operable at considerably higher revolutions per minute, and thus producing substantially higher gravities than can be achieved at present in any devices except small-volume, batch-fed tubal centrifuges.
In combination with the diameter-reducing, long residence time-enabling, and other transport efficiency geometry advantages of the Density Screening method, this method""s innovative hybrid construction approach yields a powerful and extremely flexible design methodology system which promises a harvest of multiple and significant new devices for the foreseeable future.
One additional important advantage over prior art, metal-based means of centrifuge outer wall construction relates to cost. It is anticipated that the far lower cost of laying up inexpensive PVD, CVD or other hardened wear surface parts, with comparatively inexpensive load-transfer wall or shell castings, and finally filament-winding the entire wall assembly, will quickly make possible the design and construction of centrifuges whose inner core and outer wall geometries are custom-tailored so as to provide optimized performance for even relatively low-demand, highly specialized fluid separation applications.
Especially for applications where large volume, high-gravity, or combinations of these two variables are desirable, Density Screen wall centrifuges will provide solutions where the unit cost of custom-building, or even building, conventional steel-wall decanting or disk centrifuges has never been economically viable. The inventors will be completing and filing a continuing stream of specific device and additional improvement patents, all of which shall refer back to this utility patent (method of construction) as well as to pending U.S. patent application Ser. No. 09/115,526. (geometry of the Density Screening method).
It may be of particular interest to those who study the art of invention that the fresh review of material science art described in this application was accomplished simultaneous to the inventors"" review of possible improvements to centrifuge outer wall collecting geometries, and that these two studies being done concurrently yielded unusually productive results. In other words, realizations about the complementary strengths of the hybrid sandwich materials construction literally fed and made possible radical new thinking about outer wall geometry. And conversely, novel approaches being made in that outer wall geometry thinking cross-fertilized the search for exactly the right material elements to devise the strongest, most economical and most practical-to-manufacture hybrid construction outer wall.